The application of pressure and/or thermal energy is often used to treat various medical conditions.
It is known to treat oedema by applying pressure to the limb with the oedema. For example, it is known to immerse a limb in a chamber filled with mercury in a flexible bag. Pressure is applied via the chamber of mercury to treat the oedema. More recently an improvement to this system was described in U.S. Pat. No. 4,648,392, to reduce the amount of mercury required in the chamber.
The combined application of pressure and temperature is taught in U.S. Pat. No. 5,074,285 for the treatment of sporting injuries such as bruising and muscle stiffness. In that system, thermal sources, which could be hot or cold, are introduced into pockets close to the wearers skin and pressure is applied to a series of air pockets arranged along the limb that are designed to apply a pressure-gradient repeatedly to the limb.
Hypothermia is a condition resulting from a drop in body temperature and varies in degree according to the amount of undercooling. Many methods for treating hypothermia are already known. Generally, these comprise introducing heat into the core of the body by some means to raise the body temperature. Simple treatments can take the form of a warm drink. Sometimes warm air is blown around the body via air blankets. Such a system is already well established in hospitals and marketed under the name Bair Hugger®. The system relies on heating up the periphery of the body and using the patient's blood flow to draw the heat into the core of the body.
One of the first physiological responses of hypothermia is peripheral vasoconstriction which reduces the amount of blood at the periphery of the body. This can make it difficult to introduce heat into the body through the application of heat to the body surface. It is known that vessels, including capillaries, arterioles, arteries, venoles and veins, can be made to vasodilate under conditions of negative pressure. Vasodilated skin regions, particularly on the forearm, can make efficient heat transfer surfaces.
One system that applies negative pressure to a limb to reduce peripheral vasoconstriction whilst warming the periphery of the patient to treat the hypothermia is taught in U.S. Pat. No. 5,683,438 and sold under the mark Thermostat® by Aquarius Medical Corp. In that system, a limb of the patient is placed in a sealed chamber and the pressure inside that chamber is reduced to a negative pressure of between −20 to −80 mmHg (−2.7 to −10.7 kPa). At the same time, thermal energy is delivered to the surface the limb using a thermal blanket, heat lamp or chemical heating elements. Further developments to this system are described in WO-A-01/80790.